There is a function ISBLANK() but it returns false when there's a formula in a cell even thought the formula doesn't return anything (or an empty string). I would like it to return true when the formula doesn't return anything as well. So the cell seems to be empty without any value.

I've searched the internet (Google, search tools, custom range) for references of the ISBLANK function pre-dating the OP's question. The ISBLANK function already existed during the time of asking: ISBLANK reference before 01/12/2009

Adding some more explanation as to why this answers the question would help.
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ChrisF♦Feb 10 '13 at 23:47

3

I've already described the problem with isblank() function in my question. It only returns true when cell is actually empty (not having a formula in it either). What I was looking for no content cells if that makes it more clear to you.
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Robert KoritnikFeb 12 '13 at 7:42